Storage and retrieval machines are in wide use for storage purposes in a warehouse as well as storage of components and material as part of a manufacturing facility. Many of the storage facilities are of the automated storage and retrieval type in which the operations of a number of storage and retrieval machines and associated equipment operate in a substantially unattended manner and are directed by a remote computer. Each storage and retrieval machine typically has a base which follows a guide device along aisles between vertically arranged storage racks and a mast extending vertically upward from the base and which is positioned opposite various storage racks on different levels by the appropriate positioning of the base. A carriage is mounted on the mast and is movable upwardly and downwardly on the mast for carrying a load of material or components to and from the storage racks, and a shuttle mounted on the carriage is extendible into the storage racks to deposit or retract the load from the racks.
A common type of drive for the carriage is a rope and drum drive in which a rope or cable of a steel wire type is reeved over a sheave at the upper end of the mast and has one end attached to the carriage and has the other end attached to a rotatable drum. The drum rotates to take in or pay out the rope to raise the carriage along the mast when the rope is being taken in and lower the carriage along the mast when the rope is being payed out. If the rope breaks or detaches from the carriage, or the carriage jams during lowering movement, an emergency carriage brake is provided to hold the carriage secure on the mast and prevent its uncontrolled fall. A common type of carriage brake which has been developed for this purpose includes a toothed braking cam which is positioned adjacent to a surface of the mast and is pivotally movable into engagement with the mast to brake and hold the carriage in place on the mast. The braking cam is actuated by release of a spring held in a compressed manner by tension on the rope. When the rope goes slack due to its breakage or detachment from the carriage or jamming of the carriage, the spring mechanism will release and move the braking cam into engagement with the mast. However, the reliability of this type of carriage brake to stop and hold the carriage in an emergency situation has not been satisfactory. The problems with the cam type brake have included insufficient "biting in" of the braking teeth into the surface of the mast, the failure of the braking cam to maintain tight engagement with the mast surface, and slow engagement by the cam with the mast surface and inability of the cam to adjust for variation in the location of the mast surface. The present invention is an improvement on the cam type carriage brake and is intended to address these problems.